A cross arm is provided, for use in a support structure for conductors within an electrical grid. The cross arm is made of a cementitious composite and has a rough “C” cross sectional shape. Pairs of the cross arms are attached to utility poles in a parallel position on opposite sides of the utility pole. Alternatively, a single cross arm may be attached to a utility pole. Embedded metal or glass fiber reinforced polymer bars extend along the length of the cross arms.